The /m/ sound is spelled with <m> or <mm>. The /j/ sound is spelled with <y> and occurs in the letter name U.
This is a contrast between a bilabial nasal continuant and a palatal semivowel, both voiced. The contrast only occurs initially or medially. It is not a problem.
Interesting pairs include:
The mean density value is 0.7%. The lists make 35 semantic distinctions, a loading of 58%.
ma yah ma'am yam mac yak macs yaks Manx Yanks map yap mapped yapped mapping yapping maps yaps mar yah marred yard marrow yarrow marrows yarrows mate Yate Maud yawed maul yawl mauls yawls maw yaw maws yaws maw yore maw your Max yaks May yea Mays yeas me ye mellow yellow mellows yellows mellowed yellowed mellowing yellowing mellower yellower mellowest yellowest mellowness yellowness men yen mere year mess yes messes yeses met yet mob yob mobs yobs modal yodel modals yodels moke yoke mokes yokes monger younger moo U moos U's moo you moose use mooses uses more yaw more yore more your morn yawn morning yawning morns yawns mourn yawn morned yawned mourning yawning mourns yawns myrrh year
John Higgins, Shaftesbury, December 2010.