1536, "a spark," Scottish, from Gaelic
spong "tinder, pith, sponge," from L.
spongia (see
sponge). The sense of "courage, pluck, mettle" is first attested 1773. A similar sense evolution took place in cognate Ir.
sponnc "sponge, tinder, spark, courage, spunk." Vulgar slang sense of "seminal fluid" is recorded from c.1888.
Spunky "courageous, spirited" is recorded from 1786.
[spuhngk] 
,