letting one's hair down (verb) play: have fun
Sinonime: baffling, enigmatic, incomprehensible, indecipherable, indescribable, inexplainable, inscrutable, insoluble, mysterious, mystifying, obscure, odd*, peculiar, puzzling, strange, unaccountable, undefinable, unfathomable, unintelligible, unsolvable
Antonime: work