Kesava is one of the popular names of Lord Vishnu. It is considered as Moolaroopa of the Primordial Supreme Lord (Bhagavantha).

Kesava (Ka + Eesha + Va) is the origin for and governing Lord of Brahma + Rudra;

Kesa is a Sanskrit word meaning hair or a ray of light. Kesava means the one who has got a long and beautiful hair, whose hair is very charming, filled with supreme fragrance.

Kesava is the one who is the tormentor of his enemies, and the one who’s very chanting removes sorrows and sufferings.

Without chanting of the word Kesava (Kesavaaya Namaha) none of the Vedic rituals begins.

Kesava is the slayer of demon Keshi and hence is referred as Keshiha.
Lord Sri Krishna is famously called as Kesava.

We find a reference to the word Kesava is sloka #3 and 69 of Sri Vishnu Sahasranaama Stothram.

In the context of Margasira Maasam, Kesava is its governing Lord - Maasa Niyaamaka.

Sri Krushnaarpanamasthu