Are you sure you're not thinking of σωφροσύνη? Or even εὐφροσύνη? The word θυμοσύνη is grammatically impossible, are you sure you're not misremembering what you heard? The words σωφροσύνη and εὐφροσύνη form that "frosyne" sound by their derivation from φρήν, which among other things means "mind." Whereas θυμός already means "soul," so in effect a compound of those two words would be more or less tautology