rifle vs riffle (a matter of degree or urgency)
crevasse vs crevice (a matter of size)
vocation vs avocation (a matter of wages, often)
prize vs pry (I think just a matter of British vs. Am. English)
career vs careen (a matter of direction–straight ahead or side to side [or just a matter of Am. English preference])
Confucian vs. confusion (a matter of understanding)
affluent vs. effluent (possibly a matter of odor)