専 (Kanji for specialty)

Although the onyomi of 専 is SEN, it's STRONG for HAKU or BAKU. Weird and not helpful, but, it is what it is, yo.

Onyomi

SEN

He is an international terrorist whose specialty is gluing plungers to bombs.

SEND him to headquarters, he has a new assignment!

もっぱ＊ら

exclusively, entirely, nothing but
★☆☆☆☆

専門(せんもん)

a specialty ★★★★☆
専 (specialty) + 門 (gate) = 専門 (a specialty)

専攻(せんこう)

major ★★☆☆☆
専 (specialty) + 攻 (attack) = 専攻 (major)

college major, field of study

XXX専(XXXせん)

specialist in xxx ★☆☆☆☆ SARC

someone is a specialist for XXX. In other words, they have a fetish for xxxx. Like デブ専 is a "fat person specialist"

(UTILIZE)
His specialty is TNT, but I esteem his ability to hold his SAKE - he can drink a pint and still UTILIZE a unicycle!