1. In a boyish manner.

Nuttall's Standard dictionary of the English language By Nuttall, P.Austin

• borishly,
• boreishly,
• voyishly,
• noyishly,
• hoyishly,
• goyishly,
• biyishly,
• bkyishly,
• blyishly,
• boishly,
• boyshly,
• boyishlyy,
• popishlly,
• sotishly,
• boisly,
• colishly,
• blokishly,
• bookshly,
• toyisly,
• babylishly

• boyish.

The adjective form of the word "boyishly" is "boyish".