The Lyric Thamateurge prestige class from Complete Mage has a feature at every third level titled Spell Secret. This feature grants them additional spells known as they level. The book Complete Arcane has a feat titled Extra Spell Secret that allows a caster who already has the Spell Secret class feature to permanently modify one of their spells with the Enlarge, Extend, Still, or Silent Spell metamagic feats. It seems clear that this feat was intended to be paired with the Wu Jen class's Spell Secret feature that grants the same benefits. However, is there any actual ruling that states a different class feature with the same name cannot be used to meet the prerequisite?
So far as I know, there is no official ruling on this subject. Simply put, it wasn’t supposed to happen.
The general consensus—at least among the more RAW-minded optimization community—is that a prerequisite that says you need the “xyz ability,” is only checking for an ability named “xyz,” with no regard for what that ability does or which version of that ability anyone might infer was meant. So RAW, at least, yes, a lyric thaumaturge could take Extra Spell Secret. This is very akin to “there isn’t a rule that says I can’t” kind of reasoning, though, so it’s not recommended without talking to your DM upfront about it.
Personally, I see no problem with allowing it. Lyric thaumaturge is a fairly good prestige class, but it’s not remotely overpowered on its own. You’re trading new and improved bardic music for extra spells known and extra spell slots—a decent trade, but not a free power grab. Likewise, the wu jen’s spell secret, and the Extra Spell Secret feat that gives the same effect, is pretty good, but it’s not outrageous for a feat—the only metamagic effect on offer that’s any good is Extend Spell,¹ and while that is pretty good, that’s what a feat should be.
- Not saying I would never consider one of the other options, but they are much, much more niche.