Validating Unique Columnname Across Whole Database

Option 1: Check if Column Exists in Current Database

IF EXISTS
(  SELECT *FROM sys.columnsWHERE Name = N'NameofColumn')BEGIN
SELECT 'Column Exists'-- add other logicEND
ELSE
BEGIN
SELECT 'Column Does NOT Exists'-- add other logicEND

Option 2: Check if Column Exists in Current Database in Specific Table

IF EXISTS
(  SELECT *FROM sys.columnsWHERE Name = N'NameofColumn'AND OBJECT_ID = OBJECT_ID(N'tableName'))BEGIN
SELECT 'Column Exists'-- add other logicEND
ELSE
BEGIN
SELECT 'Column Does NOT Exists'-- add other logicEND

Additional Reference:
SQL SERVER – Query to Find Column From All Tables of Database

Reference: Pinal Dave (http://blog.SQLAuthority.com)