Let, allow, permit, suffer, leave denote to refrain from preventing, or to fail to prevent, or to indicate an intention not to prevent.
Let, allow, and permit, though frequently used with little distinction of meaning, are capable of discrimination.
Let is the most informal. Sometimes let implies failure to prevent through awkwardness, inadvertence, negligence, or inaction and sometimes it implies failure to prevent through lack of power or inclination.
Allow and permit imply power or authority to prohibit or prevent.
But allow may imply little more than acquiescence or lack of prohibition, whereas permit implies express signification of willingness.
Suffer (somewhat bookish in this sense) is often a mere synonym for allow in the narrowest implication of that word, but it may imply indifference or reluctance.
Leave (see also GO 1 ) as used with the implication of letting, allowing, or permitting is not clearly distinct from the use discriminated at relinquish, but it tends to stress strongly the implication of noninterference; often it also suggests the departure of the person who might interfere.