There are minor differences in where the last stroke of the top component (top-left to bottom-right diagonal) starts – on the second horizontal stroke or on the third.
Phono-semantic compound (形聲 / 形声, *tʰun): semantic 艸(“grass”) + phonetic 屯(*dˤun;*trun;*dun, “swollen sprout”) + semantic 日(“sun”). Some oracle-bone and bronze forms contain only two components, either 艸/屮/木 with 屯, or 日 with 屯. The character may relate to a semantic cluster of its phonetic series: 蠢 (OC *tʰunʔ, “to stir”), 純 (OC *dun, “pure, unmixed”), 敦 (OC *tˤunh, “round”), and 芚 (OC *dˤun, “to sprout”).
The form 萅 preserves the older arrangement with 艸. In the regular script, the 艸 and 屯 have merged into 𡗗.
Schuessler (2007) relates it to 芚 (OC*duːn, “(of plants) to begin to grow”); he also compares it Khmerដុះ(doh, “to grow; to germinate; to sprout”), as well as 穿 (OC*kʰljon, *kʰljons, “to bore through”) (ibid.).
Sagart (2023b) relates it to a vulgar (i.e. ignoble and popular) word which means "egg", which lacked a character, whose modern reflexes are MeixianHakka春(cun1, “egg, roe”), SixianHakka春(chhûn), and Cantonese春(ceon1, “egg, roe; testicle”) (IPA: /t͡ʃʰɵn⁵⁵/); and for which he further reconstructs Old Chinese*tʰu[n] ~ *tʰu[r]. He further relates OC *tʰu[n] ~ *tʰu[r] to Bodo (India)dəy, Mizotui, Proto-Karen*ʔdejᴮ, from tentative Proto-Sino-Tibetan*tʰur, (STEDT, however, reconstructs *d(w)əy(“egg, testicle”)) and notes a connection between "eggs" and Chinese new year season, as birds generally nest and lay eggs in the warmer months in the north [1].
