Nothlit is a word in the Andalite language that describes one who has passed the two-hour morph time limit and has become trapped in that form. It is normally impossible to regain morphing ability afterwards. Two exceptions to this are Tobias and Elfangor, both regaining their forms with the Ellimist's aid. A third is Cassie, whose morphing ability was "jump-started" by the metamorphosis from caterpillar to butterfly, the naturally-occurring morphing 'resetting' the morphing clock. Nothlits who become so by choice are often shunned by Andalite society, accidental nothlits to a lesser degree. The Animorphs at several times have avoided becoming nothlits, but Tobias failed, starting in just the first book, The Invasion.
- "Tobias is what the Andalites call a nothlit. He stayed in his red-tailed hawk morph for longer than two hours. Stay in a morph for longer than two hours, and it's not a morph anymore. It's yours to keep. Now red-tailed hawk is his normal form. Although thanks to the Ellimist, he can morph like the rest of us."
While evading the Yeerks, Tobias became trapped in the form of a red-tailed hawk. He was able to regain his ability to morph in The Change, but in this case his hawk form remained his 'default' body. While he was able to regain his human form, this was the result of him being briefly sent back in time to acquire his own past self, with the result that his human body is just another morph rather than his natural state.
- "The Time Matrix was a sphere, taller than a human. Destroying it was physically impossible. But it could be hidden. For a while, at least. He found an empty place. Nothing but trees. Using only the equipment available to any human, he dug a hole and rolled the device into it. He covered it. And then, he morphed to human. Two hours later, he was no longer an Andalite. He was trapped. Human. Human forever, no longer a part of the vast war raging between Andalite and Yeerk. He was free. Or so he thought."
Elfangor voluntarily became a human nothlit, choosing a life on Earth, under the name Alan Fangor, and being married to Loren, after becoming disillusioned with the war. The Ellimist however returned him to his Andalite body, erasing most traces of his life as a human, and transported him back to the Andalite-Yeerk war.
- "You ask me to pay a terrible price to make Karen free again. Will you pay the same price? Will you become this little creature? Will you stay in that morph for two hours while I stand guard?"
"But... I would be trapped permanently!"
"Yes. Just as I will be trapped permanently."
- ―Aftran 942 and Cassie
Cassie became a caterpillar nothlit as part of a deal she made with the renegade Yeerk Aftran 942, but her new form's natural metamorphosis into a butterfly effectively reset the morph time limit, allowing her to become human again.
In an effort to prevent David from killing them and threatening to expose their identities, the Animorphs executed a plan to trap him in the body of a white rat.
- "On Aftran's second day out of the Yeerk pool, everyone in the group was well enough for a short meeting. We all agreed that we couldn't let Aftran die. It was Jake who thought of the way to save her. He suggested that we give her the power to morph, on the condition that she choose one morph and stay in it forever."
The Taxxons who served under Arbron were granted morphing ability by the Animorphs, becoming anaconda nothlits. This stemmed from the desire to end their hunger, while retaining a similar form.
- Applegate has said the word is almost an anagram of "Hilton."