The /Ɵ/ sound is spelled with <th>. The /m/ sound is spelled with <m>, <lm> or <mb>.
This is a contrast between a voiceless dental and alveolar fricative and a voiced nasal continuant. It is not a problem, although the sound /Ɵ/ is difficult for many learners.
Interesting pairs include:
nothing numbing
thistle missal
The mean density value is 0.9%. The list makes 51 semantic distinctions, a loading of 73%.
Arthur armour bath balm Beith beam Bertha Burma Cath cam doth dumb faith fame filth film filthy filmy filthier filmier filthiest filmiest firth firm firths firms forth form fourth form fourths forms froth from hath ham health helm hearth harm loath loam north norm nothing numbing oath ohm path palm Perth perm ruth rheum ruth room swath swarm teeth team thane Maine thane main thanes mains thanks Manx thatch match thatched matched thatches matches thatching matching thaw maw thaws maws thawed Maud therm mirth thews mews thews muse thigh my think mink thinks minks thistle missal thistles missals thole mole tholes moles thorn morn thorns morns thorn mourn thorns mourns thud mud thudded mudded thudding mudding thuds muds thug mug thugs mugs thumb mum thumbs mums thumps mumps tooth tomb withe whim worth worm wrath rhomb wroth Rome wroth roam
John Higgins, Shaftesbury, November 2010.