Is it farther or further?
late 14c., from Old French pustule (13c.) and directly from Latin pustula "blister, pimple," from PIE imitative root *pu- (1) "blow, swell," on notion of "inflated area" (cf. Sanskrit pupphusah "lung," Greek physa "breath, blast, wind, bubble," Lithuanian puciu "to blow, swell," Old Church Slavonic puchati "to blow"). Cf. emphysema. Related: Pustulant; pustular.
pustule pus·tule (pŭs'chōōl, pŭs'tyōōl)
A small inflamed skin swelling that is filled with pus; a pimple.
A small swelling similar to a blister or pimple.