Shorter Oxford Dictionary:
moider /ˈmɔɪdə/ verb. dial. Also mither /ˈmʌɪðə/, moither /ˈmɔɪðə/. L16.
[ORIGIN Perh. from Irish modartha dark, murky, morose, of uncertain origin.]
1 verb trans. Confuse, perplex, bewilder; worry, bother, fatigue; pester. Usu. in pass. L16.
J. O'Faolain ‘I'm a bit moidered,’ she apologized. N. Bagnall He was so moithered by the new language…that he felt he had to use it.
2 verb intrans. Work very hard, toil. rare. E19.
3 verb intrans. Be delirious; babble; wander about aimlessly, ramble. M19.
D. Winsor That phrase…kept moithering round my brain.