'Flaccid' means lacking firmness, tone, or tension, soft and limp rather than rigid or taut. Option A 'flabby' is the closest synonym, describing something that lacks firmness (commonly used for muscles or body tissue). Option B describes a centrifuge, Option C incorrectly references farewells, and Option D would describe 'vainglorious' or 'narcissistic', none of which match the meaning of flaccid.