when one person signifies to another his willingness to do or abstain from doing any thing with a view to obtaining the assent of that other person to such act or abstinence he is said to make a

The missing word in the sentence is “proposal.”

Direct answer

In contract law (e.g., Section 2(a) of the Indian Contract Act, 1872),

“When one person signifies to another his willingness to do or to abstain from doing anything, with a view to obtaining the assent of that other to such act or abstinence, he is said to make a proposal.”

So, the completed sentence is:
“When one person signifies to another his willingness to do or abstain from doing anything with a view to obtaining the assent of that other person to such act or abstinence, he is said to make a proposal.”

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