【Pressing】 ,  【urgent】 ,  【imperative】 ,  【crying】 ,  【importunate】 ,  【insistent】 ,  【exigent】 ,  【instant】  are comparable when they mean demanding or claiming attention and especially immediate attention.

【Pressing】 often implies directly or indirectly the use of pressure by persons in calling for immediate attention to their wishes, but it may also imply, without reference to personal agents, a claim to quick attention which cannot be denied.

【Urgent】  is stronger than  【pressing】 and places greater stress upon the constraint or compulsion of attention (as by a vehement urging), and it also usually connotes the need of promptness (as in replying, considering, or relieving).

【Imperative】  (see also MASTERFUL ) stresses the obligatory nature of a task, need, or duty, but it also usually implies that immediate attention is essential.

【Crying】 stresses the demand for attention but adds the implication of the extreme or shocking conspicuousness of the need.

【Importunate】 carries a strong implication of pertinacity in demanding or claiming attention; often therefore it is applied to persons or to their acts, but it is also much used in reference to impersonal matters (as problems or difficulties) which persistently and naggingly make claims upon one’s full and immediate attention.

Like  【importunate】 ,  【insistent】 basically implies a quality of persons, that of insisting or maintaining or asserting persistently and it too is often used in reference to a quality which enforces attention by its perseverance or compels it by obtruding itself upon one’s consciousness.

【Exigent】  implies less a demand for immediate attention than one for action (as by way of giving assistance or settling problems); nevertheless the term comes very close to  【urgent】  or  【pressing】 in its emphasis on the exacting or the 【imperative】 nature of that demand.

【Instant】  may come very close to  【urgent】 and like it often implies a temporal pressure; distinctively it may suggest perseverance or the need of perseverance.