Some further pairs of opposites, each with an identical number of letters:

concrete-abstract
wild-tame
ordinary-peculiar
feckless-valuable
obscure-obvious
degrade-restore
multiple-singular
withered-blooming
disgraced-respected
incendiary-refractory
scatter-collect
cling-avoid
expressive-analytical
anchor-loosen
antecedent-descendant
straight-crooked
arid-damp
angel-demon
reposed-alerted
active-torpid
tumescent-collapsed
famine-plenty
sterile-fertile
orange-indigo
comfort-disturb