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Webster 1828 Edition

Adj.

Not becoming a gentleman.

ungentlemanly ‎(comparative more ungentlemanly, superlative most ungentlemanly)

Not gentlemanly; not adhering to the high moral standards expected of a gentleman; impolite, unchivalrous, or indecent.
My grandmother thought it was ungentlemanly of my boyfriend to suggest that we split the bill for dinner.