तमस्

Tamas is one of the three modes of nature taught in the Gita, also called tamoguṇa. Its sense is inertia, darkness and fog. A mind in which tamas is strong cannot see clearly, and things simply drift or fall away.

The direct occurrence for this topic is verse 18.7, where the derived form tāmasa appears. Giving up niyata action, the duty fixed by one's own situation, is not proper; one who drops it out of delusion makes a relinquishment called tāmasa. Delusion is the fog in which duty and non-duty are not clearly seen.

The full account of the modes comes in later chapters. Here only the side that connects with the first of the three ways of letting go is in view. Note also that the verse does not carry the word tamas itself but its derived form tāmasa; the entry is kept under the name of the mode.

Common misreading: taking tamas to mean only laziness.

Better sense: tamas is fog and confusion; laziness may be one form of it, not the whole meaning.

To read further, see the topic Relinquishment and Renunciation of Action.