Seasoned wood has been dried slowly so that it is stable enough to use — seasoned oak, seasoned logs, the timber needs seasoning. Green wood warps and spits; seasoned wood does neither.
The commoner sense is about people: a seasoned traveller, a seasoned campaigner, seasoned professionals. It means experienced enough to have stopped being surprised, and it is a compliment. Both come from the same idea of something improved by time. And seasoned food is food with salt, pepper and herbs added, which is the third sense and the one a recipe means. Context separates all three without effort.
1adjectiveseasonedOf wood, dried slowly until it is stable.
“Only seasoned logs will burn properly.”
2adjectiveexperiencedExperienced and no longer easily surprised.
“Even seasoned reporters were taken aback.”
synonyms: experienced, veteran
3adjectivefoodOf food, flavoured with salt, pepper or herbs.
“The sauce is well seasoned and needs nothing else.”
Too few real examples of this word to estimate which sense is commonest.