They are nouns. Islam is a religion. Sikh is a religion. But Islam means surrender. Sikh means learn.
Knowledge is better than practice,
meditation is better
than knowledge; and best of all
is surrender, which soon brings peace.
The word Hindu is derived from the Indus River. Like Hollywood is a geographical term the word Hindu is the same way. It is terrestrial. The el in the word Israel means God. Buddhist, of course, is a follower of the Buddha. Christian is a follower of Jesus Christ, the Messiah.
The two names Islam and Sikh stand out. They are more descriptive. Surrender means loving God as completely as God loves you, which is at full capacity. It is reciprocation, or rather an attempt at it.
Ignorance is much more challenging than evil. At least evil knows God and evil knows what the sins are. Therefore, learn. Sikh.