【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.