to get into a habit; to become addicted
上 (shǎng) · 3 strokes
Originally a small line or dot above a longer line, indicating "up". The vertical line was added to distinguish the character from 二 (two). Opposite of 下.
瘾 (yǐn) · 16 strokes
Phonosemantic compound. 疒 represents the meaning and 隐 represents the sound. Simplified form of 癮.