1. Done by night or every night.

2. By night: every night.

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

• nighly,
• hightly,
• nightl,
• naighty,
• nughty,
• nightw,
• tighly,
• nightd,
• lightely,
• birghtly,
• bightly,
• nighthly,
• nightr,
• rightley,
• nightin,
• nightm,
• nighlty,
• nighte,
• naghty,
• thightly

• Nistler,
• night owl,
• nightlight,
• nightlong.

The adjective form of the word "nightly" is "nocturnal".

The plural form of "nightly" is "nightlies".

The singular form of the word "nightly" is "night"