Wiktionary
a. Not childish.
Usage examples of "unchildish".
They were delicate and finely made, some of them even beautiful, but Mab thought she could never get any pleasure out of the possession of such a frivolity, never look at it without seeing all those rows of blank, unchildish faces, and lowered eyes, and flying hands.
Eastern eyes and the mouth that showed so vividly scarlet against its unchildish pallor.
It was foolish to try to blind her, as he saw by her wan, unchildish smile.
It is true that the poor child had first been burlesqued by the unchildish aspect imposed upon him by his dress, which presented him, without the beauties of art or nature, to all the unnatural ironies.
Even as a child, Minna had seemed to her selfish and wayward, with an unchildish arrogance in her manner.
Madge put up her face and listened and gave Rue a long, unchildish look.
Clerke ceased to be put out by my asking strange unchildish questions which he was not always able to answer.
There was just the suggestion of a flush as she mentioned the name, as if she had some unchildish memory.
Havisham saw him sitting in some queer little old-fashioned attitude, watching the sea, with a very grave face, and more than once he heard an unchildish sigh rise to his lips.