What is the ONE WORD that describes the biggest challenge facing today's senior HR professionals?

The biggest challenge facing senior HR professionals today is

(EXPECTATIONS)

Talent Retention............................

Strategy   

(Answer should contain minimum25 characters) 

My word would be 

IMPARTIAL 

Organizational Strategy ...............................................

My 1st  word would be Harassment.

      2nd word would be Conflict.

      3rd word would be Stress.

Leadership Development - As companies grow and expand, developing leaders who are efficient, is a necessity. Leadership development also connects to retention in two ways. Employees often indicate poor managerial leadership as a reason for leaving jobs. Additionally, employees want more active leadership roles for decision making, within their departments, which may also necessitate training. Unfortunately, businesses sometimes struggle to come up with the budgets necessary for strong employee training and development programs that emphasize leadership and growth, where they are expected to provide essential framework,processes,tools and point of view for selection and development of future leaders.

Talent - acquisition, engagement and retention

"Change" :) !!! (Quite a few of the above answers too are right, and actually it would depend in what perspective you've asked) !!!

Despite some of the correct answers above, I would say the One Word challenge could be "THE INEQUALITY"... Inequality in size between Jobs' Market and Jobs' Applicants

enabling a strong-self learning culture.