Legitimate is an adjective describing something or someone being genuine or of real value, permitted by a set of rules or laws. In one case, it is used to describe a child as being born of parents who were married, though this use is a little out-dated.
This can also be a verb, legitimated or legitimating, and it means the action of making something or someone legitimate according to the definition above. It has two noun forms, legitimation and legitimator.
Legitimize is simply another verb form of legitimate, a more popular and accepted form. It has two noun forms, legitimization and legitimizer.
The alternate form has been around since the 1850s, while the original was coined in the 1500s.
Legitimise is a variant spelling for places outside of the US, though in the European dictionaries we checked, the z spelling was the official entry.
On the one hand, “Halabja” has become discursive shorthand for the suffering of all Kurds and a kind of cornerstone legitimating the need for Kurdish self-rule. [The Washington Post]
“The individual is the legitimator of religious practice” in the US. [The Times of Israel]
The Mavericks were hoping Rondo would be the element that could work well with what they already had and legitimize their shot at this season’s championship. [Boston Herald]
The change “has legitimized us in front of the whole world,” he said after the meeting, per the report. [CBS Sports]
The state’s hotel legitimisation process started in March last year where illegal hotels were told to apply for one-year temporary permits pending their application for full licenses. [The Malay Mail]