1. Attentively.

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

• ibservingly,
• kbservingly,
• lbservingly,
• pbservingly,
• 0bservingly,
• 9bservingly,
• ovservingly,
• onservingly,
• ohservingly,
• ogservingly,
• obaervingly,
• obzervingly,
• obxervingly,
• obdervingly,
• obeervingly,
• obwervingly,
• obswrvingly,
• obserbingly,
• obsevringly,
• obseveingly

• observantly,
• observant,
• observable,
• observatory,
• observation,
• observably,
• observing,
• observed,
• observer.

The adjective form of "observingly" is "observant".

The plural form of "observingly" is "observingly" as it is an adverb and does not have a distinct plural form.

The singular form of the word "observingly" is "observing"