Нечитаемые (немые) согласные.

-bt[t] doubt, debt -alk[ k] walk,talk,chalk

-mb[m] comb, climb -alf [a:f] half,calf

-gn [n] sign, foreign -alm [a:m] calm,palm

-ps[s] psychology, psalm -mn[m] autumn, condemn

-stle[sl] wrestle, castle, whistle kn[n]know, knife