V$RESERVED_WORDS
Data Dictionary ViewColumns ___________________________ KEYWORD LENGTH
Examples
-- Find a keyword:
select keyword
  from V$RESERVED_WORDS 
  where keyword ='pctincrease';
-- Examples of reserved words/keywords that throw an error:
SQL> create table user(test varchar2(10));
  create table user(test varchar2(10))
  *
  ERROR at line 1:
ORA-00903: invalid table name
SQL> create table test(user varchar2(10));
  create table test(user varchar2(10))
  *
  ERROR at line 1:
  ORA-00904: : invalid identifier
  -- Examples of reserved words/keywords that don't throw an error :
  -- (these can still cause problems)
SQL> create table type(sid varchar2(3), id varchar2(3), data varchar2(3));
Table created.
-- Find any tables, views etc with reserved words:
SQL> select 
  object_name,object_type,owner,keyword
  from dba_OBJECTS,v$reserved_words 
  where object_name=keyword
  and owner = 'MY_SCHEMA';
  
Table created.
-- Find columns in any table with reserved words:
select
  table_name,column_name,owner,keyword
  from dba_TAB_COLUMNS,v$reserved_words 
  where column_name=keyword
and owner = 'MY_SCHEMA';
If you run the two scripts above against the SYS schema you will find many system views and tables which contain reserved words and keywords. This is to be expected - they are 'reserved' for use by Oracle.
In addition to reserved words, Oracle implicitly generates system names beginning with "SYS_" Oracle discourages you from using this prefix.
Related: