meaning

Webster's Dictionary of Synonyms, first edition (1942) addresses cowardly and pusillanimous in an entry that also includes the allied terms poltroon, craven, dastardly, and recreant:

Cowardly, pusillanimous, poltroon, craven, dastardly, recreant agree in meaning excessively timid or timorous. Cowardly, the most general term, implies a weak or ignoble, pusillanimous a mean-spirited and contemptible, lack of courage; as, "He...plac'd behind With purpose to relieve and follow them, Cowardly fled, not having struck one stroke" (Shak[espeare]); "Cowardly dogs! ye will not aid me then?" (Shelley); "I lived in a continual, indefinite pining fear; tremulous, pusillanimous, apprehensive of I knew not what (Carlyle); "having no materialized class above it, it {American vulgarity} is not obsequious and pusillanimous" (Brownell).

Interestingly, Merriam-Webster's Dictionary of Synonyms (1984), the successor to the first edition of Webster's Dictionary of Synonyms, drops all coverage of cowardly, pusillanimous, craven, dastardly, and the rest. The omission is all the more inexplicable in view of the fact that Merriam-Webster's Ninth Collegiate Dictionary (1983) includes the following usage note at the end of its entry for cowardly:

COWARDLY, PUSILLANIMOUS, CRAVEN, DASTARDLY mean having or showing a lack of courage. COWARDLY implies a weak or ignoble lack of courage; PUSILLANIMOUS suggests a contemptible lack of courage; ...

In its usage note, the Eleventh Collegiate Dictionary (2003)—the most recent in the series—adds examples of cowardly ("a cowardly failure to stand up for principle") and pusillanimous ("the pusillanimous fear of a future full of possibility") but otherwise retains the same description of each that appears in the Ninth Collegiate. So either the lexicographers at Merriam-Webster consider the difference between "a weak or ignoble lack of courage" and "a contemptible lack of courage" to be fundamental and obvious or they haven't bothered to revisit the distinction since they set it down back in 1942, even as the Dictionary of Synonyms branch of the organization has withdrawn from the discussion altogether.

S.I. Hayakawa, Choose the Right Word: A Modern Guide to Synonyms (1968) offers this commentary on cowardly and pusillanimous, which it discusses along with craven:

cowardly craven pusillanimous These words mean lacking courage to a degree that arouses disapproval and disgust. Cowardly is the most common word of the three, and is applied opprobriously to persons who are unwilling or unable to prevent their fear or timidity from influencing their actions unduly; it can also refer to the actions themselves: In frontier days, shooting a man in the back was considered cowardly; too cowardly to stand up and fight.

Craven and pusillanimous are formal words encountered mainly in writing. ... Pusillanimous differs from the other terms in in pointing more strongly to temperamental timidity than to fear as the basis of the resulting action or inaction. Pusillanimous represents a contemptible moral squeamishness rather than a physical cowardliness, although it is quite possible for the same person to be both pusillanimous and cowardly. What chiefly distinguishes the pusillanimous person, however, is his unwillingness to press for his rights: His pusillanimous reaction was to sigh and say, "Well, it really won't do to raise a fuss."

These various attempts to distinguish between cowardly and pusillanimous touch upon several possible points of difference:

1. Cowardly is a more general term and is therefore applicable to a broader range of situations.

2. Pusillanimous is a more literary term and is therefore less likely to be encountered on the streets of Laredo.

3. There is some sense that cowardly may apply to situations where the act (or failure to act) is understandable, though it fails to meet even a minimum standard of appropriate conduct under the circumstances; that is, in some cases, it may apply to an uncharacteristic but explicable failure of nerve and thus indicate a temporary shortcoming. Pusillanimous, on the other hand, seems to go to a habit of mind—a fundamental, ever-present lack of bravery that leads to cowardly behavior even when meeting an acceptable standard of conduct wouldn't require unusual fortitude or high-mindedness; this would explain the association (by both Merriam-Webster and Hayakawa) of contemptible with pusillanimous but not (or not necessarily) with cowardly.