Its parts

• 囟 xìn fontanel (gap between the bones of an… meaning
• 比 bǐ to compare = 匕 + 匕 sound

Other characters with 比 as their sound:

批 pī毕 bì屁 pì庇 bì毙 bì毗 pí纰 pī琵 pí

In other characters

Gives the sound in

媲 pì貔 pí

Also in

鎞 bì